Diets based on the glycaemic index (Gl) have become popular. They focus on the role of carbohydrates (sugary and starchy foods) in the diet, and particularly on the speed at which carbohydrates are digested into glucose and released into the bloodstream.
The glycaemic index (Gl) is a way of classifying carbohydrates according to how quickly they are digested. Glucose, which is rapidly dispersed into the bloodstream, has a Gl rating of 100, while grapefruit has aGI of 14 and spaghetti a Gl of 41.
This was developed by nutritionists researching into diabetes, which occurs when the body's ability to produce insulin and regulate glucose is impaired. A key part of managing the condition is to keep glucose levels stable, and researchers found that carbohydrates that are digested slowly cause fewer peaks and troughs in glucose levels than those that release glucose quickly into the blood.
People with diabetes are often advised to include low-GI carbohydrates with each meal as part of their treatment plan. People who do not have diabetes do not need help with managing their glucose and insulin levels. But further research into the Gl classification has found that it can play an important role in helping to manage weight.
The theory behind Gl weight loss diets is that filling up on carbohydrates with a low Gl helps to control overall energy intake, because they are more likely to keep hunger at bay for longer than other foods. High-GI carbohydrates, by contrast, are believed to produce a short-lived 'sugar rush' followed by a dip in energy and the desire to eat again. Slimmers who are following a low-GI plan are less likely to eat high-sugar, high-fat snacks, and to eat low-fat, high-fibre meals, so that it should be possible to create a calorie deficit resulting In a weight loss at the desirable rate of 450-900 g (1-2 lb) a week.
One reason why the low-GI diet has become very popular with nutritionists is that many of the principles are in line with current thinking on what makes a healthy diet. Low-GI carbohydrates (with a rating below 60) include most fruit and vegetables, wholemeal stoneground bread, porridge, rice and pulses. They are likely to be high in fibre, either soluble or Insoluble, which is good for the digestive system and heart health, and many -although not all – are low in sugar and fat.
High Gl foods, which are to be limited or avoided on a Gl weight loss diet, include white bread, white rice, sugary breakfast cereals, and foods made with sugar or white flour such as cakes and biscuits. Processed foods like these are also likely to include saturated fats or trans fats, which need to be limited.